AWS Crash Course – RDS

Welcome to AWS Crash Course.

What is RDS?

  • RDS is Relational Database Service of Amazon.
  • It is part of its PaaS offering.
  • A new DB instance can easily be launched from AWS management console.
  • Complex administration process like patching, backup etc. are manged automatically by RDS.
  • Amazon has its own relational database called Amazon Aurora.
  • RDS also supports other popular database engines like MySQL, Oracle, SQL Server, PostgreSQL and MariaDB .

RDS Supports Multi AZ(Availability Zone) failovers.

What does that mean?

It means if your primary DB is down. Services will automatically failover to secondary DB in other AZ.

  • Multi-AZ deployments for MySQL,Oracle and PostgreSQL engines utilizes synchronous physical replication to keep data on the standby up-to-date with Primary.
  • Multi-AZ deployments for the SQL server engine use synchronous logical replication to achieve the same result, employing SQL server native mirroring tech.
  • Both approaches safeguard your data in event of a DB instance failure or loss of AZ.
  • Backups are taken from secondary DB which avoids I/O suspension to the primary.
  • Restore’s are taken from secondary DB which avoids I/O suspension to the primary.
  • You can force a failover from one AZ to another by rebooting your DB instance.

But RDS Multi AZ failover is not a scaling Solution.

Read Replicas are for Scaling.

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What are Read Replicas?

As we discussed above Multi AZ is synchronous replication of DB.  While read replicas are asynchronous replication of DB.

  • You can have 5 read replicas for both MySQL and PostgreSQL.
  • You can have read replicas in different regions but for MySQL only.
  • Read replica’s can be built off Multi-AZ’s databases.
  • You can have read replica’s of read replica’s , however only for MySQL and this will further increase latency.
  • You can use read replicas for generating reports. By this you won’t put load on the primary DB.

RDS supports automated backups.

But keep these things in mind.

  • There is a performance hit if Multi-AZ is not enabled.
  • If you delete an instance then all automated backups are deleted, however manual db snapshots will not be deleted.
  • All snapshots are stored on S3.
  • When you do a restore , you can change the engine type(e.g. SQL standard to SQL enterprise) provided you have enough storage space.

Hope the above snapshot give you a decent understanding of RDS. If you want to try some handson check this tutorial .

This series is created to give you a quick snapshot of AWS technologies.  You can check about other AWS services in this series over here .

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